Mass spectrometry systems are analytical systems used for quantitative and qualitative determination of the compositions of materials, which include chemical mixtures and biological samples. In general, a mass spectrometry system uses an ion source to produce electrically charged particles (e.g., molecular or polyatomic ions) from of the material to be analyzed. Once produced, the electrically charged particles are introduced to the mass spectrometer and separated by mass analyzer based on their respective mass-to-charge ratios. The abundance of the separated electrically charged particles are then detected and a mass spectrum of the material is produced. The mass spectrum is analogous to a fingerprint of the sample material being analyzed. The mass spectrum provides information about the mass-to-charge ratio of a particular compound in a mixture sample and, in some cases molecular structure of that component in the mixture.
For determining molecular weight of a compound, mass spectrometry systems employing a single mass analyzer are widely used. These analyzers include a quadrupole (Q) mass analyzer, a time-of-flight mass analyzer (TOFMS), ion trap (IT-MS), and etc. For more complicated molecular structure analysis, however, tandem mass spectrometers (Tandem-MS or MS/MS) are often needed. Tandem mass analyzers typically consist of two mass analyzers of the same or of different types, for instance TOF-TOF MS or Q-TOF MS. In a tandem MS analysis, ionized particles are sent to the first mass analyzer and an ion of particular interest is selected. The selected ion is transmitted to a dissociation cell where the selected ion is fragmented. The fragment ions are transmitted to the second mass analyzer for mass analysis. The fragmentation pattern obtained from the second mass analyzer can be used to determine the structure of the corresponding molecules.
For example, in a triple quadrupole mass spectrometer an ionization source produces a plurality of parent ions. The first quadrupole mass analyzer is used to select a particular parent ion. Then, the selected parent ion is dissociated into daughter ions in the second quadrupole via photodissociation and/or collisionally induced dissociation. Subsequently, the third quadrupole mass analyzer is used to separate the daughter ions based on their respective mass-to-charge ratios. The resulting mass spectrum can be used to identify the daughter ions, which can be useful in identifying the structure of the selected parent ion.
In the example described above, the second quadrupole can be used as a collision cell to facilitate collision induced dissociation of the selected parention. When the parent ions collide with a background gas (normally an inert gas such as argon), a portion of the translation energy of the parent ions is converted into activation energy that is sufficiently high to break certain molecular bonds. The fragment pattern produced characterizes the original molecule and provides information about its structure.
In the example described above, a laser can be used to photodissociate the parent ions in the second quadrupole instead of collisions with gas molecules. Current photodissociation techniques use a cross-directed laser beam and a complex mirror system or an on-axis directed laser beam to create a high photon flux to dissociate the molecular ions. However, these photodissociation techniques require expensive high power lasers (e.g., CO2 laser). Cross-directed laser beam techniques require precision mirror alignment, which can be expensive and time consuming to achieve. On-axis directed laser beam techniques are problematic because of significant ion loss.
Thus, there is a need in the industry for a mass spectrometry system that uses a photodissociation technique that overcomes at least these disadvantages.
Embodiments of the present invention provide for mass spectrometry systems and methods of use. Briefly described, one embodiment of the mass spectrometry system, among others, includes a radio frequency multipole assembly, an inner structure, and a laser diode array system. The inner structure has an outer surface, an inner surface, and an opening. The inner structure substantially surrounds the radio frequency multipole assembly. The laser diode array system is disposed on the outer surface of the inner structure adjacent the opening such that laser radiation emitted from the laser diode array system travels through the opening.
Embodiments of the present invention also include methods for dissociating an ion. In this regard, one embodiment of such a method, among others, includes producing an ion and focusing the ion into a dissociation cell/laser diode array system. The dissociation cell/laser diode array system includes a radio frequency multipole assembly, a structure that substantially surrounds the radio frequency multipole assembly and a laser diode array system disposed on the outer surface of the structure. The method also includes producing laser radiation with a laser diode array system and photodissociating the ion.